The U.S. has sentenced three Chinese men to federal prison for attempting to export technology with potential military applications to China, the U.S. Department of Justice said Tuesday.

In separate cases, two of the men were charged with attempting to export thermal-imaging cameras, and a third was charged with illegally exporting hundreds of integrated circuits that could be used in military radar systems, the department said in a statement.

The men, all from Beijing, were given prison terms of between 20 months and five years in rulings handed down starting last week. Their exports to China were illegal without clearance from the U.S. Department of Commerce because the items have both military and non-military uses, the statement said.

In the case of the integrated circuits, prosecutors argued that the defendant was using a front company in the U.S. to ship items to his company in Beijing, it said. A catalog from the man's Beijing company was found to carry pictures of military craft and state a goal of helping "facilitate the building of the national defense of China," the statement said, citing the sentencing brief.

Prosecutors also argued that the man supplied restricted U.S. technology to several Chinese customers, including one linked to a state-owned company that makes missile systems and spacecraft.

The two men in the thermal cameras case were arrested at the Los Angeles airport last year after 10 of the cameras were found in their luggage, either stuffed in their shoes or hidden in their packed clothes. The cameras are contained in two-inch cubes and are sensitive enough to detect heat on an object too small to be seen by the naked eye, the statement said.

The U.S. has imprisoned and fined multiple Chinese nationals over military technology exports to China in recent years. Defendants in those cases have attempted to export technology including fighter jet components and night vision equipment.

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